The present invention relates generally to one-way drive devices and, more particularly, to methods of making such devices by means of integral stamp forming.
Example of an excellent prior art one-way drive device is described in the U.S. Pat. No. 5,070,978 (the Pires Patent), which is incorporated herein by reference. For the convenience of the reader, FIGS. 5, 5A, 6 and 7 are illustrated here as FIG. 1. Note that both the figure numbers and the reference numerals from the Pires Patent have been retained in the present FIG. 1. What is illustrated in this group of figures is a one-way drive device 60, which includes a strut or pocket plate 74 and a receptor or notch plate 76, which are mounted for rotation about axis 63 in confronting relationship to one another. The pocket plate 74 is shown including a pocket 88 in its confronting surface while the notch plate 76 is shown including a notch 92 in its confronting surface. In fact, while not shown in the specific figures of the Pires Patent shown in FIG. 1, the actual device described there includes a number of pockets 88 and a number of notches 92 (see, for example, FIGS. 8 and 9 in the Pires Patent). A strut assembly including a strut 94 and biasing spring 104 is shown mounted with the pocket plate so as to allow the strut to move between (i) the first position (FIG. 6 in the Pires Patent) so as to allow the pocket plate 74 to rotate about axis 63 in one direction relative to notch plate 76, and (ii) a second position (FIG. 7 in the Pires Patent) in simultaneous engagement with opposing shoulders formed by pocket 88 and notch 92 so as to prevent the pocket plate from rotating about axis 63 in the opposite direction relative to the notch plate.
For a more detailed description of one-way drive number 60, reference is made to the Pires patent itself. It suffices here to note that in an actual commercial embodiment of the one-way drive device described in the Pires Patent, the pocket plate 74 and the notch plate 76 are molded from powered metal, this being the preferred method of making the device by its manufacturer. In a similar vein, the pocket plate and the notch plate could be and have been formed by means of machining those parts. In either case, the one-way drive device formed by these methods has found great success in the marketplace and, technically speaking, has been found to operate quite reliably for its intended purpose. Nevertheless, as will be seen hereinafter, Applicants have discovered a way of manufacturing the one-way drive device much more economically while retaining its technical integrity. More specifically, Applicants have discovered that both the pocket plate and the notch plate can be made by means of integral stamp forming rather than by means of molding or machining and still produce a technically acceptable one-way drive device.
A more particular method of manufacture contemplated by Applicants has been the use of fine blanking, which is illustrated in FIG. 2 and which is well known in the art. Therefore, this process, which is generally indicated at 200 will not be described in detail. It suffices merely to note that the work piece 202, for example, a pocket plate or a notch plate, is positioned between opposing guide and die plates 204 and 206, respectively, having the appropriate passageways corresponding to the pockets or notches to be stamped formed. To this end, cooperating punches 207 and ejectors 208 are provided for establishing blanking and counter pressures. Again, this process is well known in the art and hence will not be described further herein.
What is to be noted, however, is the prior belief by those with ordinary skill in the art, at least to Applicants' knowledge, that such an approach, that is stamp forming, would make it quite difficult to achieve at least commercially the desired “resolution” of the one-way drive device required by a one-way drive device (to be explained below) as compared to one manufactured by means of molding or machining. To illustrate this best, reference is made to FIGS. 3A-D. FIGS. 3A and B illustrate a notch plate 210 corresponding to previously discussed notch plate 76 forming part of the Pires device shown in FIG. 1. Notch plate 210, which is manufactured either by means of molding or machining, is in turn shown including a series of notches 212 circumferentially or annularly spaced around the outer periphery of the notch plate along its surface 214 that would confront the corresponding surface of a cooperating pocket plate. Note, in particular, that a relatively large number of notches can be provided owing to the fact that they can be positioned relatively close to one another as a result of the molding or machining process. The nature of these processes allows the space between notches to be minimized. FIGS. 3C and D illustrates a similar notch plate 210A, but one which is manufactured by means of fine blanking utilizing the process described in conjunction with FIG. 2. In this case, the notches 212A that are stamped into the surface 214A are spaced further from one another than the notices 212. Nevertheless, and quite surprising to Applicants, for a given notch plate size, a sufficient number of notches can be readily stamped formed such that the resolution of the overall device is not compromised beyond an acceptable limit.
What is meant by the resolution of the one-way drive device is the rotational back travel of the clutch in which the first one of the struts of the one-way drive device locks within a notch, thereby locking the notch and pocket plates together. The more pockets and notches that can be provided, the more often a strut can lock in place and the greater the resolution of the device. Again, to Applicants' surprise, from the standpoint of resolution, an acceptable one-way drive device can be made by means of stamp forming as compared to its molded or machined counterpart.
Another concern has been that the stamp forming process would weaken the notches in the notch plate due to the thinning of the notch plate walls resulting from that process. To explain this concern in more detail, attention is directed to FIGS. 3B and 3D. FIG. 3B is the sectional view (B-B) of the molded or machined notch plate illustrated in FIG. 3A. Note in particular the notch plate between adjacent notches is quite thick. Actually it retains the initial thickness of the notch plate. This is to be contrasted with the notch plate 210A shown in section (A-A) in FIG. 3D. Note, in particular, the material between and adjacent to each of the notches is thinner than the total thickness of the notch plate due to the effect of stretching of the material as a result of the stamp forming process. Applicants discovered this thinness does not compromise the structural integrity of the notch plate to an unacceptable limit. Indeed, Applicants have found that an overall one-way drive device can be manufactured quite economically using stamp formed pocket and notch plates while retaining the structural and technical integrity required to compete with its molded or machined counterpart.
Moreover, as will also be seen, in order to ensure its technical success, the stamp formed one-way drive device disclosed herein has been provided with certain novel technical details that are compatible with this more economical method of manufacturing the device.